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Transcript of Optical fiber

  • 1.Laser Applications
    • By
  • Khurshid Aslam Bhatti
  • Department of Physics
  • UET, Lahore

2. LASER

  • Lasers play a pivotal role in our everyday lives
  • Alaseris a device that emits light (electromagnetic radiation) through a process called stimulated emission.
  • The term "laser" is an acronym forLight Amplification by Stimulated Emission of Radiation.

3. Properties ofLaser Light

  • Laser light is very different from normallight .
  • Monochromatic:One specific wavelength (Color) determined by the amount of energy released when the electron drops to a lower orbit.
  • Coherent:Organized -- each photon moves in step with the others. All of the photons have wave fronts that launch in unison.
  • Directional:A laser light has a very tight beam and is very strong and concentrated. A flashlight, on the other hand, releases light in many directions, and the light is very weak and diffuse.

4.

  • To make these three properties occur takes something calledstimulated emission . This does not occur in ordinaryflashlight-- in a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized.

5. Photon Absorption and Emission 6. Spontaneous and Stimulated Emission 7. Population Inversion For a laser you need a continuous number of available electrons for transition to a lower state emitting photons. In equilibrium most systems have a Boltzmann distribution of states and therefore the ground state always has the largest number of electrons. By electrical or optical pumping, carriers can be excited to higher states and the population of the states can be changed. For lasing, the upper radiative transition states must have a large population of electrons than the ground state i.e. population inversion. This also requires thelifetimesof each state to be correct to allow population inversion. (Most lasers, however, use four levels with a fast depopulation of the lower radiative transitions state but it is easier to illustrate population inversion using a three level laser system). 8. 9.

  • Key to a laser is a pair ofmirrors , one at each end of the lasing medium.
  • Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium.
  • In the process, they stimulate other electrons to make the downward energy jump and can cause the emission of more photons of the same wavelength and phase.
  • A cascade effect occurs, and soon we have propagated many, many photons of the same wavelength and phase. The mirror at one end of the laser is "half-silvered," meaning it reflects some light and lets some light through.
  • The light that makes it through is the laser light.

10. DIFFERENT STEPS

  • A laser makes light by passing electricity through a gas.
  • This makes the gas emit (give out) light waves at a precise wavelength.
  • The light waves bounce back and forth along a tube between two mirrors.
  • This encourages the gas to give out more light exactly in step with the original light waves. It also amplifies (makes brighter) the beam of light

11. Three-Level Laser 12.

    • Laser mode is the possible standing em waves in laser cavity.
    • Longitudinal (Axial) Modes
      • Axial standing em waves within the laser cavity.
      • Laser Resonator or Laser Cavity
        • The optical mirrors,active mediumand pumping system form thelaser resonator , which is also called Laser Cavity. Laser cavities can be divided into Stable Cavities and Unstable Cavities according to whether they make the oscillating beam converge into the cavity or spread out from the cavity.

13. Types of Lasers

  • Lasers are designated by the type of lasing material employed:
  • Solid-state Lasers:Lasing Material Distributed in a Solid Matrix ruby or Nd:YAG (Neodymium: Yttrium- Aluminum Garnet ;1,064 nm).
  • Gas Lasers:He, HeNe, Most common gas lasers; visible red light. CO 2lasers emit energy in the far-infrared, used for cutting.
  • EXCIMER lasers:(the name is derived from the termsexcitedanddimers ) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as Ar, Kr or Xe. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet range.
  • Dye lasers:use complex organic dyes, such as rhodamine 6G, in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.
  • Semiconductor lasers:diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, such as the writing source in somelaser printersorCD players .

14. Wavelengths of Lasers

  • Here are some :
  • Laser Type Wavelength (nm)
  • Argon fluoride (UV) 193
  • Krypton fluoride (UV) 248
  • Xenon chloride (UV) 308
  • Nitrogen (UV) 337
  • Argon (blue) 488
  • Argon (green) 514
  • Helium neon (green) 543
  • Helium neon (red) 633
  • Rhodamine 6G dye (tunable) 570-650
  • Ruby (CrAlO 3 ) (red) 694
  • Nd:Yag (NIR) 1064
  • Carbon dioxide (FIR) 10600

15. Laser Classifications

  • Class I- These lasers cannot emit laserradiationat known hazard levels.
  • Class I.A.- This is a special designation that applies only to lasers that are "not intended for viewing," such as a supermarket laser scanner. The upper power limit of Class I.A. is 4.0 mW.
  • Class II- These are low-power visible lasers that emit above Class I levels but at a radiant power not above 1 mW. The concept is that the human aversion reaction to bright light will protect a person.
  • Class IIIA- These are intermediate-power lasers (cw: 1-5 mW), which are hazardous only for intrabeam viewing. Most pen-like pointing lasers are in this class.
  • Class IIIB- These are moderate-power lasers.
  • Class IV- These are high-power lasers (cw: 500 mW, pulsed: 10 J/cm 2or the diffuse reflection limit), which are hazardous to view under any condition (directly or diffusely scattered), and are a potentialfirehazard and a skin hazard. Significant controls are required of Class IV laser facilities

16. MEDICAL USE

  • The use of lasers has revolutionized medicine because lasers are accurate, quick, and minimally invasive.There are six different types of laser-tissue interaction illustrated in figure .
  • The accuracy of the laser assures that only the desired portion of a specimen is affected by the laser.
  • The strength of the laser provides any medical treatment with adequate power to ablate the plaque, no matter how large the obstruction may be.
  • The efficiency of the laser provides a better medical treatment because it takes less repetitions of the treatment to complete the procedure.

17. TYPES OF LASER TISSUE INTERACTION

  • There are six different types of laser-tissue interaction illustrated as.
  • Heat
  • Photochemistry
  • Photoablation.
  • Florescence
  • Ionization.

18. IN MEDICAL 19. APPLICATIONS OF LASERS

  • In medical
  • Military
  • Industrial and commercial
  • Atmospheric

20. 21. 22. A laser beam fired into the heart can help people suffering from angina pectoris. 23. Lasers can be used to correct defects of the lens and cornea as well as repair tears and holes in the retina. 24. MATERIAL PROCESSING

  • Laser cutting,
  • Laser welding,
  • Laser brazing,
  • Laser bending,
  • Laser engraving or marking,
  • Laser cleaning, weapons etc.

25. CUTTING 26. ADVANTAGES OF LASER CUTTING

  • Cutting edges are tight and parallels
  • Reduced Heat Affected Zone
  • Possibility to operate on complex profiles and reduced curving radius
  • Absence of mechanical distortion of the laser worked piece
  • No influence of the hardness of the material
  • No problems to cut materials prevoiusly coated

27. DRILLING Blind hole obtained by using an excimer laser beam on CFCPassing hole obtained by using an excimer laser beam on CFC 28. 29. IN MILITARY

  • Target designation and ranging,
  • Defensive countermeasures,
  • Communications
  • Directed energy weapons.
  • such as Boeings Airborne Laser which can be mounted on a 747 jet is able to burn the skin off enemy missiles .

30. A long range laser rangefinder LRB20000 is capable of measuring distance up to 20 km; mounted on a tripod with an angular mount. The resulting system also provides azimuth and elevation measurements.Alaser rangefinderis a device which uses a laser beam in order to determine the